There are known gear pumps each including a drive gear and a driven gear meshing with each other. In such a gear pump having meshing gears each configured as a helical gear, end portions of the gears are pressed onto a side plate by a thrust force produced by the meshing of teeth of the gears and a thrust force due to hydraulic pressure exerted on tooth surfaces of the gears. This may cause a disadvantage such as wearing out of the end portions of the drive gear and the driven gear, and reduction in mechanical efficiency due to friction.